Abstract
Bone morphogenetic protein-2 (BMP-2) stimulates osteoblastic differentiation in human periodontal ligament cells (HPDL cells). This action of BMP-2 is modulated by prostaglandin E2 (PGE2), which is local regulatory factor in bone metabolism. In the present study, we investigated mechanisms involved in enhancement by PGE2 of BMP-2-stimulated osteoblastic differentiation in HPDL cells. PGE receptor (EP) 2 agonist and EP4 agonist as well as PGE2 enhanced the BMP-2-stimulated Alkaline phosphatase (ALP) activity. PGE2, EP2 agonist and EP 4 agonist, but not BMP-2, stimulated cyclic AMP (cAMP) accumulation, and cAMP-elevating agents such as forskolin, dibutyryl cAMP (db-cAMP) and 3- (isobutyl) -1- methylxantine (IBMX) were enhanced the BMP-2-stimulated ALP activity. The PGE2-enhanced ALP activity in HPDL cells treated with BMP-2 was inhibited by adding a protein kinase (PK) A inhibitor H89, whereas, a PKC inhibitor GF109203X had no effect on it. H89 also inhibited the enhancement by EP2 agonist or EP4 agonist of BMP-2-stimulated ALP activity. EP2 agonist, EP4 agonist, forskolin and db-cAMP stimulated phosphorylation of CREB, whereas, BMP-2 had no effect on it. On the other hand, BMP-2, but not EP2 agonist, EP4 agonist, forskolin or db-cAMP, stimulated phosphorylation of Smad 1. These results suggest that PGE2 enhances BMP-2-stimulated osteoblastic differentiation in human periodontal ligament cells via EP2/4-cAMP/PKA signaling cascade.
